1. Field of the Invention
The present invention relates to a packaging structure of planographic printing plates and an internal packaging material for the planographic printing plates. More specifically, the present invention relates to a packaging structure of planographic printing plates, which can block the planographic printing plates from light from the exterior and can protect the plates from an external force, and to an internal packaging material for the planographic printing plates, which can block the planographic printing plates from light from the exterior and can internally package the plates.
2. Description of the Related Art
In electrophotographic plate making methods in recent years, in order to facilitate automation of plate making processes, planographic printing plates such as photosensitive printing plates or thermosensitive printing plates have been widely used. The photosensitive printing plates have high photosensitivity, and thus, even if the plates are exposed to a slight amount of light within a visible light wavelength band, a change is caused in photosensitive layers thereof. Therefore, the photosensitive printing plates need to be blocked from light. Similarly, in the thermosensitive printing plates, thermosensitive layers thereof may be deteriorated by thermal energy of light striking thereon, or a sensitivity change may be caused by a reaction progress. Therefore, it is preferable that the thermosensitive printing plates are appropriately blocked from light. Further, if the photosensitive or thermosensitive printing plates are subjected to rapid changes in humidity and temperature, there is a drawback in that, for example, dewing is caused in the photosensitive or thermosensitive layers thereof and the layers are thereby deteriorated. Therefore, these printing plates need to be kept free from moisture.
Accordingly, from the time when the planographic printing plates are manufactured to the time when the plates are loaded into an automatic plate making machine or the like, the planographic printing plates are packaged in an internal packaging paper which has a light-blocking property and a moisture-proofing property (i.e., the property of keeping the plates packaged therein free from moisture). As the internal packaging paper, for example, an aluminum kraft paper, in which low density polyethylene is melted and applied at a thickness of about 13 xcexcm on a kraft paper, and then aluminum foil having a thickness of about 6 xcexcm is further adhered thereon, is used. A stack of products (a stack of the planographic printing plates) are packaged in this aluminum kraft paper, and thereafter, portions (so-called ear portions and top surface portions) of the aluminum kraft paper are fastened by an adhesive tape or other fastening means. Further, as the internal packaging paper, a paper in which low density polyethylene is adhered at a thickness of about 10-70 xcexcm on the aluminum foil of this aluminum kraft paper, or a paper in which black polyethylene film is further adhered at a thickness of about 70 xcexcm on this low density polyethylene so as to increase the light-blocking property and the moisture-proofing property, is also used.
However, this aluminum kraft paper cannot be recycled once it has been used, and since it becomes necessary to dispose of the paper by dumping it as industrial waste, or by incineration or the like, the disposal requires a high expense.
On the other hand, a light-blocking and moisture-proofing paper which has the required light-blocking and moisture-proofing properties without the aluminum foil adhered thereon, has been suggested (see Japanese Patent Application Laid-Open (JP-A) No. 9-111697). However, this light-blocking and moisture-proofing paper becomes expensive, because a light-blocking layer and a moisture-proofing layer must be provided on the surface thereof.
Moreover, each of the photosensitive printing plates and the thermosensitive printing plates is formed in a single thin plate, and thus, if there is a blemish or deformation in a corner, an edge, an interior or the like thereof, problems are easily caused. For example, an image may be unclear when the plate has been developed after light-exposure or the plate has been developed with heat, or ink may not be uniform when the image has been printed.
Therefore, in order to prevent such blemishes or deformations, a corrugated cardboard box, which protects the planographic printing plates from an external force and packages the plates, has been suggested (see Japanese Patent Application Laid-Open (JP-A) No. 10-16946).
As shown in FIG. 10, in a corrugated cardboard box 50, triangular tube-shaped bodies 54 are formed by bending two opposite sides of a bottom surface panel 52, and thereby the perpendicularity of the bottom surface panel 52 to side surface panels 56 and to facing panels 58 is strongly maintained. In this way, the corrugated cardboard box 50 is structured so as not to lose its shape due to the weight of its contents.
However, in this corrugated cardboard box 50, light comes inside from the vicinities of the triangular tube-shaped bodies 54, fastened portions of the corrugated cardboard, and the like. Accordingly, when the planographic printing plates are contained in the corrugated cardboard box 50, there is the danger that so-called accidental exposure (light fog) can occur in the planographic printing plates.
In consideration of the above facts, it is an object of the present invention to obtain a packaging structure of planographic printing plates, which can reliably protect the planographic printing plates from an external force, which can block the plates from light and keep the plates free from moisture, and which can be disposed of easily and inexpensively; and an internal packaging material for the planographic printing plates, which can reliably block the planographic printing plates from light.
A first aspect of the present invention is a packaging structure of planographic printing plates, the structure comprising: an internal packaging material, which is made from a material having a light transmittance of predetermined value or lower, and which internally packages the planographic printing plates; and an external packaging material, which externally packages the planographic printing plates that have been internally packaged in the internal packaging material, and which has a higher rigidity than the internal packaging material.
Namely, the planographic printing plates, which have been internally packaged in the internal packaging material, are externally packaged in the external packaging material which has a higher rigidity than the internal packaging material. Therefore, the planographic printing plates are protected from an external force, and thus, the plates are not deformed or blemished.
The external packaging material can block the planographic printing plates from light and keep the plates free from moisture to some extent by itself. As a result, in a state of being externally packaged in the external packaging material, only a minuscule amount of light enters through very small gaps in the external packaging material to the interior thereof.
Because the planographic printing plates are internally packaged in the internal packaging material which is structured of a material having a light transmittance of a predetermined value or lower, even if there is such light-leakage, the light does not reach the planographic printing plates, and thus, changes in the photosensitive or thermosensitive layers of the planographic printing plates are prevented.
Further, even if there is a large change in humidity outside the external packaging material, a change in humidity in the interior of the external packaging material is small, because the external packaging material functions as a buffer. In the interior of the internal packaging material, a small change in humidity in the interior of the external packaging material is further buffered. Therefore, problems resulting from changes in humidity, such as dewing and the like are not caused in the planographic printing plates, and thus, the photosensitive or thermosensitive layers thereof are not deteriorated.
In this manner, by using a combination of the internal packaging material and the external packaging material, the planographic printing plates are reliably blocked from light and kept free from moisture such that the quality thereof is not effected. As the internal packaging material, any materials having a light transmittance of a predetermined value or lower can be used. Accordingly, a general paper or the like, which can be easily disposed of, can be used in place of the conventional aluminum kraft paper or the like, and thus, the planographic printing plates can be packaged at a low cost.
As long as the above-described conditions are satisfied, the material forming the internal packaging material is not particularly limited. For example, a general paper which can be recycled is preferably used. As a result, because the used internal packaging material can be recycled as a recyclable material, the planographic printing plates can be packaged without wasting resources. Examples of the general paper which can be recycled can include recyclable general paper, to which a layer or structure having a light-blocking or moisture-proofing effect is not particularly provided or attached.
A specific value of the light transmittance of the internal packaging material is determined based upon the sensitivity of the photosensitive or thermosensitive layers of the planographic printing plates, the intensity of light filtering in through gaps in the external packaging material and the like. However, the planographic printing plates can be more reliably blocked from light by preferably using an internal packaging material whose light transmittance is 57% or lower with respect to light having a wavelength of 910 nm or shorter in a state in which the planographic printing plates are internally packaged.
With regard to the light transmittance, if the total light transmittance of the internal packaging materials satisfies the above-mentioned value in a state in which the planographic printing plates are internally packaged in the internal packaging materials, there is no problem. For example, even though a single sheet of an internal packaging material might have a light transmittance of 57% or higher with respect to light having a wavelength of 910 nm or shorter, if the planographic printing plates are internally packaged in layers of the internal packaging materials with the resultant light transmittance in the state of internally packaging being 57% or lower, there is no problem. In other words, even though a single sheet of the internal packaging material might have a light transmittance of 57% or higher with respect to light having a wavelength of 910 nm or shorter, if each light transmittance is determined so that the resultant light transmittance is 57% or lower by using layers of the internal packaging materials, all of such internal packaging materials can be included in the xe2x80x9cinternal packaging materialxe2x80x9d referred to herein.
As long as the external packaging material can protect the planographic printing plates from an external force so as to prevent deformations or blemishes thereof by having a higher rigidity than the internal packaging material, the material forming the external packaging material is not particularly limited. For example, the external packaging material may be made of corrugated cardboard. The internally packaged planographic printing plates can thereby be reliably protected from an external force such that blemishes or deformations effecting the quality of the plates do not arise. In addition, the combination of the external packaging material and the internal packaging material is able to reliably ensure the necessary light-blocking and moisture-proofing properties such that the quality of the plates is not effected. As normal corrugated cardboard can be used as the external packaging material, the planographic printing plates can be packaged at a low cost.
A second aspect of the present invention is an internal packaging material for planographic printing plates for internally packaging the planographic printing plates, wherein a light transmittance of the internal packaging material is 57% or lower with respect to light having a wavelength of 910 nm or shorter.
Accordingly, the planographic printing plates can be reliably blocked from light by applying the internal packaging material to the above-described packaging structure of the planographic printing plates.
Also in the internal packaging material for the planographic printing plates according to the second aspect of the present invention, with regard to the light transmittance, if the total light transmittance of the internal packaging materials satisfies the above-mentioned value in a state in which the planographic printing plates are internally packaged in the internal packaging materials, there is no problem. For example, even though a single sheet of an internal packaging material might have a light transmittance of 57% or higher with respect to light having a wavelength of 910 nm or shorter, if the planographic printing plates are internally packaged in layers of the internal packaging materials with the resultant light transmittance in the state of internally packaging being 57% or lower, such internal packaging materials are included in the internal packaging material for the planographic printing plates according to the second aspect of the present invention. In other words, even though a single sheet of an internal packaging material might have a light transmittance of 57% or higher with respect to light having a wavelength of 910 nm or shorter, if each light transmittance is determined so that the resultant light transmittance is 57% or lower by using layers of the internal packaging materials, all of such internal packaging materials can be included in the xe2x80x9cinternal packaging materialxe2x80x9d referred to herein. In a case in which the planographic printing plates are internally packaged in a plural number of internal packaging materials, not only internal packaging materials each of which has the same light transmittance, but also internal packaging materials each of which has a different light transmittance may be used. The number of layers of the internal packaging materials is not particularly limited. However, from the viewpoints of enabling an internal packaging with fewer sheets of material, of facilitating an internal packaging operation and an unpacking operation, and the like, it is preferable that about two to four sheets of internal packaging material are overlaid.